Hand held power tools are quite commonly used today, both by workers in various fields of industry and by individuals employing such tools for home use, as well as for hobbies. Such hand-held tools have inherent, although correctable, dangers. For instance, hand-held circular power saws have a saw blade which must necessarily be exposed in order to perform a cutting operation. These saws are generally activated by the operator depressing a finger trigger-type switch within the handle. At times, although not making a cut, the exposed blade will still rotate due to the operator's continued grip of the trigger on the saw handle. Serious harm results with contact between the blade and the operator's body. For this reason, saw manufacturers have placed rotatable blade guards on virtually all the hand held circular saws in use today. These rotatable guards are spring energized, biased to close the guard over the saw blade. When force is placed on the guard, for instance through contact with a workpiece, the rotary blade is exposed, The guard will then telescope into a preformed chamber surrounding the saw blade.
The rotatable guard has an inherent deficiency as it presently exists. It is the object of this invention to eliminate this deficiency without destroying the saw's utility. The deficiency lies in the fact that the saw blade can be exposed, with risk of injury to the operator, as a consequence of an unintended guard reopening. Previous guards were designed to open whenever the saw was advanced upon the workpiece. Those guards, however, will also open if the saw is unintentionally advanced upon any part of the operator's body. This can and does happen when a kickback occurs, causing the operator to lose control over the saw, allowing the saw to come in contact with the operator's body causing reopening of the guard. During such an occurrence the blade continues to rotate under power since the operator invariably maintains or increases his grip on the saw's handle, with his finger on the switch trigger, as he attempts to maintain control over the saw. The present invention controls this reopening of the blade guard which, in turn, controls the exposure of the saw blade and thereby prevents injury to the operator.
Two previous references of which the inventor is aware have dealt with the problem of the blade guard on a saw. U.S. Pat. Nos. 1,811,577 (Crowe) and 1,813,231 (Crowe) both contain a blade guard which is spring loaded to cover the exposed blade of a circular saw. Yet, both inventions do not encompass the rotatable guards present in modern circular saws. Nor do these inventions contain a mechanism which ensures that the blade guard continues to cover the saw blade once kickback has occurred and the spring loaded guard has returned to its protective position.